I'm guessing this thread has been done before, but if so, certainly not within the past ~5 years or so. As such, I'd like to get the ball rolling on the 2019 version.

Allow me to get the party started with my own current assessment. Note that my data set applies almost exclusively to domestic/regional economy flights

BIG FOUR
1. China Eastern (MU)
-as recently as 10 years ago, I couldn't have fathomed the idea of putting MU in the top half of my list, much less the pole position
-but, I have to admit that they have made GREAT STRIDES across the board
-their 77Ws and A330s are really nice airplanes in all classes
-their 320s are more comfortable than 737s
-free wifi on all flights that have wifi
-slightly better than average service/food
-in addition to being my top pick among the big four, they are also my go to airline ex-Shanghai

2. China Southern (CZ)
-many would (and do) argue that CZ is better than MU because they run a pretty tight ship
-furthermore, they are the biggest of the big four, and the gap is likely increase significantly if/when their PKX plan materializes (CAN/SZX, WUH, and URC aren't useful for most of us)
-I'm a fan of their (substantially) extra legroom seats in economy
-their planes are fairly solid across the board, but none of them are really mind blowing
-food and service are both okay

3. Air China (CA)
-CA retains more "SOE" culture than MU and CZ (not so good), but has been lifted by its tight partnership with CX (good)
-like MU, they place cool airplanes (e.g. 744s) on the PEK-SHA route
-their narrow body planes (mix of 737s and 320s) are okay enough
-food is a little disappointing...not really an issue for me
-I can't really fault them for service, but it's unlikely to blow anyone away

4. Hainan (HU)
-it may (or may not) be surprising that I place HU in last place among the big four
-while I realize that their 787s are pretty damn comfortable, their cabin crews try hard, and their unconventional ways are refreshing, my gut always dissuades me from booking their flights
-basically, I regard them as a "wild, wild, west" airline, which is cool from an innovation standpoint, but doesn't instill confidence in me
-I shall also note that I started flying HU in 1995 (for real!), when they were really loopy, so I suppose some of these past prejudices have endured

SHANGHAI BASED AIRLINES
(since I'm based in Shanghai, I feel compelled to opine on these in isolation)
1. China Eastern (MU)
-see above for my general comments, but when they fit my schedule, I pick them

2. Spring (9C)
-sure, their seats are painful, they fly at crazy time slots, and they are a true ULCC
-the thing is, their staff is awesome across the board (i.e. EXTREMELY nice people); just watch a few of their Youtube/Youku videos, and you'll get the picture
-pay the extra Y100 to sit in a non-horrible seat, and you will survive
-note: price is usually a constant in these parts (e.g. MU and CA match fares), but 9C doesn't really care about this; as such, my assessment most definitely takes ROI into account

3. Shanghai Airlines (FM)
-when I first started flying a lot within China (~2000), FM was a standout carrier (i.e. easily top pick on the PEK-SHA route)
*they had the best planes, FAs, and food
*they were a little more reliable than the big guys
-after MU bought them, they started to go downhill...in a big way
-I flew them back from NNG tonight on a 738, in which they had ripped out the first class section (for captive markets like NNG), they didn't serve any substantial food, and they parked the plane at a pretty far away remote stand (though, not at T1, which is a common docking point for the same flight)

4. Juneyao (HO)
-I've never been a fan
-while their 320s aren't especially uncomfortable, the operation itself doesn't engender a great deal of confidence
-in spite of how much I've grown to dislike FM, I still prefer them to HO at this point in time

In closing, apart from the above, I have thoughts on other Chinese airlines, some of which I like, but I want to close out this initial post here.